1. Field of the Invention
The present invention relates to material testing apparatus for testing physical properties of test specimens, and in particular, it relates to testing apparatus wherein the loads applied to the testing specimens are measured in the crosshead member.
2. Description of the Prior Art
Material testing equipment is used to test the physical characteristics of materials such as metals or plastics. The materials are cut into test specimens according to established standard testing procedures. The test specimens are then placed in the load frame and are held by grips and tested under tension and/or compression loads. In the case of a test specimen tested under tension, data is obtained to develop relationship such as a stress/strain curve wherein physical properties such as elasticity, yield and fracture toughness, among others, are measured. Typical material testers are produced by MTS Systems Corporation of Minneapolis, Minn. and are illustrated in its catalog entitled, "MTS Interactive Material Test System Catalog." Although the typical test frame, such as is manufactured by MTS Systems Corporation, satisfactorily tests test specimens, there is a need for improving the accuracy of testing such test specimens, conserving space and reducing cost.
In the MTS test frames, but upper grip that holds the test specimen is a stationary grip and is attached to a crosshead member which is clamped onto supporting posts. The grip is attached to the crosshead through a load cell which measures load forces encountered during a testing cycle. The load cell takes up valuable vertical space between the crosshead and the upper grip, extending the height of the machine and limiting the amount of space for testing the test specimen.
In addition, the crosshead member needs to be attached to the upright supports of the testing machine such that it can be adjusted to accommodate specimens of various lengths and such that no movement of the crosshead member which could interfere with the load cell measurements occurs during a testing cycle. Hydraulically operated clamps presently are used on crosshead members. The crosshead may be held with other clamps or methods of securing the crossheads, such as threaded columns, shrink lock clamps, and nonadjustable or fixed crossheads may be used.